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#Post#: 120688--------------------------------------------------
Marginal Speeding Offence - Accuracy of Equipment
DIR By: RTB_
Date: June 4, 2026, 6:26 am
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Good Afternoon.
I've just received a NIP from Surrey Police for an offence of
57.3mph in a 50mph zone, by an automatic camera device.
This is obviously a very marginal offence as, using the 10% +
2mph rule the minimum speed you can get prosecuted for is
57.0mph.
I've gone onto their website and viewed the evidence, as well as
the calibration certificate for the camera. However, the
calibration certificate does not state the accuracy/measurement
uncertainty of the equipment. Any given item of measuring
equipment has a certain stated figure for accuracy/measurement
uncertainty, as nothing can be infinitely accurate. If the
measurement uncertainty of the device in question was, for
example, +/- 0.5mph then in my eyes the prosecution isn't valid,
as I may have been going only 56.8mph, for example.
Would it be prudent to request this information, and how should
I go about doing this?
Thanks
#Post#: 120691--------------------------------------------------
Re: Marginal Speeding Offence - Accuracy of Equipment
DIR By: RichardW
Date: June 4, 2026, 6:41 am
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10% + 2 is only the guidance for the start of enforcement; you
can be prosecuted at 0.1 (or less) over the limit.
#Post#: 120692--------------------------------------------------
Re: Marginal Speeding Offence - Accuracy of Equipment
DIR By: JustLoveCars
Date: June 4, 2026, 6:41 am
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So you 'admit' to 56.8mph in a 50mph limit?
I think you can see where this is heading... (I wouldn't call
13% over the limit as 'marginal')
The very threshold you refer to is to avoid such 'marginal'
arguments.
As noted above, a prosecution can succeed for anything over the
limit but in reality would not be pursued if it was 1mph or 2mph
- most devices may publish an accuracy as +/-1 mph but are
actually more accurate than that. Indeed, the cosine effect can
actually under report true speed anyway.
You are not going to escape an allegation of 57.3mph on this
basis. (Indeed, it's unusual that the allegation is so
accurate, it's usually whole mph only)
#Post#: 120693--------------------------------------------------
Re: Marginal Speeding Offence - Accuracy of Equipment
DIR By: andy_foster
Date: June 4, 2026, 6:55 am
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--- Quote from: RTB_ link ---
>
> This is obviously a very marginal offence as, using the 10% +
2mph rule the minimum speed you can get prosecuted for is
57.0mph.
>
--- End Quote ---
Please don't lie to us.
As explained in the "READ THIS FIRST" post (which you clearly
didn't), not only are the guidelines merely that (guidelines),
but the purpose is to enable the court to be certain that the
motorist was actually exceeding the speed limit. The guidelines
apply to the recorded speed, not the recorded speed minus some
theoretical tolerance.
#Post#: 120712--------------------------------------------------
Re: Marginal Speeding Offence - Accuracy of Equipment
DIR By: NewJudge
Date: June 4, 2026, 8:26 am
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--- Quote ---
> This is obviously a very marginal offence as, using the 10% +
2mph rule the minimum speed you can get prosecuted for is
57.0mph.
--- End Quote ---
Hmmm. Interesting.
If you read all of the guidance (rather than just the bits which
suit your purpose) you will find this:
5. Disposal Thresholds for Speeding Offences
5.1 Thresholds for disposal options are included in this
guidance so that police forces can be consistent in their
approach when dealing with those committing speeding offences.
5.2 While this is a transparent approach, it has also resulted
in the creation of a pseudo speed limit with many drivers
understanding that they are unlikely to face any enforcement
action unless they are speeding well beyond the posted limit,
35mph in a 30mph limit or 68mph in a 60mph limit, for example.
5.3 Nothing in this guidance restricts police forces from
prosecuting for speeds falling below the thresholds. [My
emphasis] However, such decisions should be taken on a
case-by-case basis with due regard to the individual
circumstances of the offence and relevant signage and
engineering in place at the time.
Also included in the guidance is the rationale behind the
thresholds:
HTML https://library.college.police.uk/docs/NPCC/Speed-enforcement-disposal-guidance-2025.pdf
--- Quote ---
> Would it be prudent to request this information,
--- End Quote ---
No. The police are very unlikely to engage in correspondence and
you already have more material than they are obliged to give you
at this stage. The idea of a course or fixed penalty (which you
will be offered) is that you accept the allegation as it stands.
If you want to make a technical defence you will have to plead
not guilty in court and show that the device cannot be relied
upon to prove you were exceeding the speed limit. If you decide
to do that, do let us know how it goes.
Do not forget that whatever you decide to do, you must respond
to the request for driver’s details within the 28 days allowed
let us know
#Post#: 120728--------------------------------------------------
Re: Marginal Speeding Offence - Accuracy of Equipment
DIR By: RTB_
Date: June 4, 2026, 10:44 am
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Thanks all. Understood.
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